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Maternal Oxygen Affects Nonreassuring FHR Patterns

Am Fam Physician. 2007 Jan 1;75(1):111.

Background: One of the options for resuscitating fetuses with nonreassuring fetal heart rate (FHR) patterns during labor is to use maternal oxygen supplementation. However, various studies have found inconsistent results with this intervention. Fetal pulse oximetry was developed to provide an accurate reading of fetal oxygenation during labor, and two studies that used fetal pulse oximetry to determine the effect of maternal oxygen supplementation on fetal oxygen saturation showed inconsistent results. The studies were small, varied in their study design, and evaluated the effect of maternal oxygen supplementation in a fetus with reassuring FHR patterns. This suggests that the fetus in the study probably had normal oxygenation and that oxygen supplementation likely did not increase fetal oxygen saturation. Haydon and colleagues evaluated the effect of maternal oxygen supplementation on fetal pulse oximetry during labor in fetuses with nonreassuring FHR patterns.

The Study: Participants in the study were women from two medical centers who were in active labor with a singleton pregnancy at a gestational age of 36 weeks or more and had ruptured membranes, cephalic presentation, and a cervical dilation greater than 2 cm. To participate, they had to have nonreassuring FHR patterns defined as: 1) decreased variability; 2) late decelerations; 3) persistent late decelerations; 4) mild-to-moderate variable decelerations; or 5) tachycardia. All who participated had intravenous fluids at the same rate of 125 mL per hour and were placed in the left or right lateral decubitus position. The first part of the study consisted of 30 minutes of room air (fraction of inspired oxygen [FIO2] 21 percent) followed by 30 minutes of 6 L per minute (FIO2 40 percent) of oxygen via face mask. This was followed with another 30 minutes of room air and then 30 minutes of 10 L per minute (100 percent FIO2) of oxygen via nonrebreather face mask. Fetal oxygen saturation was measured continuously throughout the study.

Forty-six women were enrolled, but 22 did not complete the study because of emergent cesarean delivery or precipitous delivery. The mean age of participants was 29.4 years, the mean gestational age was 39.7 weeks, and the mean neonatal birth weight was 3,143 grams. All Apgar scores were 7 or higher at one and five minutes except in one newborn whose Apgar scores were 5 at one minute and 8 at five minutes.

Results: The mean increase in fetal oxygen saturation was 4.9 percent for 40 percent FIO2 and 6.5 percent for 100 percent FIO2. In fetuses with an initial oxygen saturation of 30 to 40 percent, the increases in saturation were 7.0 percent for 40 percent FIO2 and 12.6 percent for 100 percent FIO2. Fetuses with the lowest initial oxygen saturation had the greatest improvement in their oximetry readings. All of these increases were statistically significant compared with room air oximetry levels. These results were consistent regardless of which of the five nonreassuring FHR patterns were present.

Conclusion: The authors conclude that providing supplemental oxygen to women in labor significantly increases fetal oxygen saturation in fetuses with nonreassuring FHR patterns. They add that those with the lowest oxygen saturation seem to benefit the most from maternal oxygen supplementation.